AP automatic transmission

The AP automatic transmission is a 4-speed automatic transmission unit developed by Automotive Products and the British Motor Corporation specifically for use in the Mini.

It was unique in that not only was it one of the first transverse mounted automatic transmission units tailored for front wheel drive, it was one of the smallest in order to be used in the transmission-in-sump installation beneath the A-series engine used in the Mini, and later the 1100/1300 ranges. Another novel feature was that the transmission was designed to use the engine's lubricating oil, rather than conventional automatic transmission fluid (ATF). The units were manufactured in a BMC plant in Kings Norton, Birmingham which supplied complete powertrain packages (the unit required a unique engine variant) to the Longbridge and Cowley assembly plants.

It was also later used on the Austin Allegro, and its final use was in the original version of the Austin Metro, and remained an option until 1990.

Known Issues

- Because the unit uses engine oil for both lubrication and for powering its hydraulic circuit, engine oil changes are critical to the long term reliability of the transmission. Typically it should be changed every 6000 miles.

- The transmission is not interchangeable with a conventional BMC sump mounted manual gearbox. Because of an extended flywheel mounting flange on the crankshaft, the AP automatic requires to be fitted to its own unique version of the A-series engine. This causes issues for Mini owners wanting to convert to a manual gearbox, since the entire engine has to be changed also.

-Due to the design of the transmission, the main forward clutch had to take the engine torque AFTER multiplication through the gearbox. As a result, forward clutch failure was common.

Applications

Mini (1967–1981) BMC ADO16 (1967–73) Austin Allegro (1973–82) Austin Metro (1980–1990)

References

https://web.archive.org/web/20131018030057/http://www.austinmemories.com/page172A/page172.html